When listening to music, watching movies and the like, generally, speakers and the like are used to reproduce acoustic information. Although such the speakers can reproduce the acoustic information with audible frequencies, the large size speakers are required in order to efficiently reproduce (air vibration) sound with a low frequency range whose frequency is in a range of 20 [Hz] to 200 [Hz].
On the other hand, not only auditory sense but also somatic sense of a whole body can be contributed in perception of the sound in the low frequency range. Particularly, it is said that a sense of presence is high by using the auditory sense in combination with the somatic sense in listening to music by using headphones or the like.
Thus, recently, a system that utilizes body sensible acoustic which alternates the presentation of the acoustic signal with the conventional auditory sense stimulation and presents the acoustic signal via the somatic sense, or presents the acoustic signal with the combination of the auditory sense stimulation and the somatic sense.
In the system that utilizes the above somatic sense, for example, there exists the system that enhances the sense of presence to the music by feeling the sound, the low frequency components of the music and the like as the acoustic vibration to the user by means of bone vibration and the vibration to a body trunk or the body.
In the above body sensible acoustic system, for example, instead of generating the sound by vibrating the air, a converter that converts the electric signal into the mechanical vibration such as an electric-mechanical vibration converter which is disclosed in Japanese Unexamined Patent Publication No. H07-323068 A (Patent Document 1), is used.
In a technology described in the above Patent Document 1, as shown in a side cross-sectional view of FIG. 14A, an elastic member having rigidity that is withstood to the load of the weight of the human body is used as a casing 2 of the electric-mechanical vibration converter 1. In this casing 2, a magnetic circuit 6 that comprises a yoke 4 and a magnet 5 is loosely fitted via a damper 3. A support 8 of a coil 7 that is faced on a magnetic space of the yoke 4 is attached to the casing 2. The electric signal that is inputted into the coil 7 is converted into the mechanical motion by magnetic action, and then the casing 2 vibrates.
As examples that such the converters are used, a relaxation chair disclosed in Japanese Unexamined Patent Publication No. 2001-212198 A (Patent Document 2) that transmits the vibration to the user who sits thereon, an attachable body sensible vibration apparatus disclosed in Japanese Unexamined Patent Publication No. H08-116581 A (Patent Document 3) and the like are known.
Here, in the above Patent Document 2, as shown in a perspective view of FIG. 14B, the relaxation chair 11 that comprises plural vibration members 10 which convert the acoustic signal into the vibration sound for relaxation is described. In the above Patent Document 3, as shown in a perspective view of FIG. 14C, the attachable body sensible vibration apparatus 12 is described. Shoulder pads 14 are connected to a waist pad 13 via length adjustable belts, a waist belt 15 is provided with the waist pad 13 and is formed with a harness type to fix the human body to the waist pad 13, and the electric-mechanical vibration converters 16, which generate the vibration generally consistent with waveforms of the voice signal against the voice signal electric-converted the voice with the audible range, are attached to the shoulder pads 14 and the waist pad 13.